The present invention relates to a seat hinge device which freely permits angular movement of a seat back relative to a seat bottom under normal circumstances but prevents the angular movement in case of an emergency. The present invention also relates to a vehicle seat using such an emergency locking seat hinge device
A vehicle seat is often provided with a seat hinge device for permitting an angular movement of a seat back relative to a seat bottom. typically for permitting the adjustment of the angle of the seat back for the best comfort of the vehicle occupant. Japanese patent laid open publication No. 10-234507 discloses a seat hinge device of this type which permits an angular adjustment of the seat back in a continuous manner as opposed to the more conventional ratchet gear type adjustment mechanism which is capable of angular adjustment only in a discrete manner. Also, the seat back may be required to be folded forward to permit access to the rear compartment of the vehicle, and a seat hinge device may be used for such a purpose. In either case, a locking mechanism or a latch mechanism is provided in association with the hinge device to fixedly secure the angular position of the seat back under normal conditions, and to selectively permit free angular motion of the scat back when so desired. Typically, such a hinge device is provided only on one side of the seat while the other side of the seat is provided with a normal hinge device which freely permits angular motion at all times.
A known disadvantage with such a system is that there is a significant difficulty in attaining an adequate mechanical strength to the locking mechanism for the hinge device. For instance, the seat back may be pushed forward by an object in the rear compartment when the vehicle sharply decelerates due to an abrupt braking or a crash. Because the seat back is restrained only on one side, the seat back may produce a tendency to twist. and the seat back. as well as the locking mechanism, is required to have an adequate mechanical strength and structural rigidity to withstand such a force. In case of a vehicle seat in which the upper end of the shoulder belt is attached to the seat back, the tension in the belt may apply a significant forward force to the seat back in a high deceleration situation. Similarly, when the vehicle is hit by another vehicle from the rear, the inertia of the vehicle occupant will apply a significant rearward force to the seat back.
For the locking mechanism for the seat hinge device to be capable of withstanding such a force, the locking mechanism is required to be made of relatively bulky and massive components, and this creates serious layout problems in addition to aesthetic problems. It is conceivable to provide a hinge device equipped with a locking mechanism on each side of the vehicle seat to ensure a sufficient mechanical strength. However, this requires a rod extending between the two hinge devices to synchronized the locking action of the two hinge devices, and this takes up a significant space under the seat. It is also conceivable to synchronize the locking action of two hinge devices by using a cable mechanism or other flexible force transmitting media as an alternative measure, but it would complicate the system, and increase the cost.
In view of such problems of the prior art, a primary object of the present invention is to provide an emergency locking seat hinge device which allows free angular motion of the scat back under normal conditions, but can fixedly secure the angular position of the seat back at any desired angular position in a continuous manner in high deceleration or acceleration situations.
A second object of the present invention is to provide an emergency locking seat hinge device which is simple in structure, and economical to fabricate.
A third object of the present invention is to provide an emergency locking seat hinge device which is highly compact.
A fourth object of the present invention is to provide an emergency locking seat hinge device which can maintain the angular position of the seat back even when subjected to a relatively large force.
According to the present invention, these and other objects can be accomplished by providing an emergency locking seat hinge device, comprising: a seat bottom bracket adapted to be attached to a seat bottom and defining an annular recess therein; a seat back bracket adapted to be attached to a seat back. and pivotally attached to the scat bottom bracket about an axial center of the annular recess; an inner cam member integrally attached to the seat back bracket and received in the annular recess so as to jointly define a plurality of chambers each having a relatively wide central part and end parts which get progressively narrower circumferentially away from the central part, a plurality of rolling members each received in a corresponding one of the chambers, each rolling member being dimensioned so as to be narrower than the central part but wider than the end parts; a disk member which is pivotally and coaxially supported by the seat back bracket and provided with a plurality of projections for engaging each of the rolling members; spring members provided between the disk member and the inner cam member for producing a circumferential centering spring force therebetween which resiliently retains the rolling members in the wide central parts via the projections of the disk member; and an acceleration sensitive locking device which engages the disk member with respect to the seat bottom bracket upon detection of an acceleration or deceleration exceeding a prescribed level.
Thus, upon detection of an acceleration or decelration exceeding a prescribed level, a relative angular displacement is produced between the disk member and the inner cam member. As a result, the rolling members arc displaced from the wide central parts toward the narrower ends parts. Therefore, when a relative rotation occurs between the seat back bracket and the seat bottom bracket as a result of the acceleration or deceleration, the rolling members are wedged between these two members, and prevent the relative rotation between the seat bottom bracket and the seat back bracket. This locking action can take place at any desired angular position as opposed to the locking action of a ratchet device which can prevent relatively rotation only at prescribed discrete angular positions
Therefore, it is particularly advantageous to provide the scat hinge device only on one side of the seat while a recliner hinge device is provided on the opposite side of the scat. Thus, the hinge device does not interfere with the normal adjustment of the seat back by the recliner hinge device, but in a high acceleration situation such as a vehicle crash, the hinge device of the present invention opposes the angular motion of the seat back in cooperation with the recliner device at a high mechanical strength without causing any significant deformation to the seat back. The present invention is equally applicable to a foldable seat which has a seat back adapted to be folded forward to permit access to the rear compartment of the vehicle. In this case, a hinge device with a latch is provided on one side of the scat while the hinge device of the present invention is provided on the other side of the scat.
Also, the hinge device of the present invention can prevent the relative rotation of either direction between the seat back and the seat bottom.
According to a preferred embodiment of the present invention, the acceleration sensitive locking device comprises at least one ratchet wheel provided in the disk member, a pawl member moveably supported by the seat bottom bracket so as to selectively engage the ratchet wheel, and an inertia mass member resiliently supported by the seat bottom bracket and adapted to drive the pawl member into engagement with the ratchet wheel when subjected to an acclamation or declaration exceeding a prescribed level. The inertia mass member can be resiliently supported in a number of different ways which arc all well known in the art. For instance, a metallic ball may be placed in a bottom of a valley so that the motion of the metallic ball moving up the slope in a high acceleration or deceleration situation may be used for activating the pawl member, with the gravitational force providing the resilient force for maintaining the metallic ball at the rest position. Also, a pendulum or a mass supported by a spring member may also be used instead of the metallic ball.
Likewise, the spring members provided between the disk member and the inner cam member for producing a circumferential centering spring force therebetween may take a number of different forms without departing from the spirit of the present invention. According to a preferred embodiment of the present invention, the disk member is provided with an arcuate slot, and the inner cam member is provided with an axial projection received in the arcuate slot, the spring members including a pair of compression coil springs each interposed between the axial projection and a corresponding one of the circumferential ends of the arcuate slot.
It is important that the inner cam member is securely attached to the seat back bracket without interfering with the pivotal connection between the seat back bracket and the seat bottom bracket. According to the preferred embodiment of the present invention, the scat back bracket is provided with an opening surrounded by a collar which is fitted into an opening defined in the scat bottom bracket coaxially with respect to the annular recess so as to pivotally support the seat back bracket with the seat bottom bracket. Further, the opening in the seat back bracket is provided with an inner circumferential profile in the shape of an internal gear, and the inner cam member is also provided with a central opening having an identical inner circumferential profile, a gear member having a corresponding outer profile being fitted into the openings of the seat back bracket and the inner cam member with an annular shoulder defined by the annular recess of the scat bottom bracket interposed between the inner cam member and the seat back bracket.
According to a particularly preferred embodiment of the present invention, the collar of the seat back bracket is provided with an outer circumferential profile in the shape of an external gear, and the inner cam member is provided with a plurality of axial projections arranged along a common coaxial circle which fit into gaps defined between the inner circumferential surface of the opening of the seat bottom bracket and the outer profile of the collar of the seat back bracket.
A flanged sleeve member may be passed through a central opening of the gear member, and the central bore of the disk member so that the entire assembly of the hinge device. more particularly the seat bottom bracket can be securely attached to a seat frame by passing a threaded bolt though the inner bore of the sleeve.
Once the rolling members are wedged between the inner cam member and the seat bottom bracket, the presence of the projections for retaining the rolling members in the center of the chambers is no longer necessary. Therefore, the projections of the disk member for engaging the rolling members may be adapted to be destroyed when the disk member is engaged by the acceleration sensitive locking device, and the rolling members are wedged into the narrow end parts of chambers.